A polarity pathway for exocyst-dependent intracellular tube extension.

Joshua Abrams,Jeremy Nance

doi:10.7554/elife.65169

Abstract

Lumen extension in intracellular tubes can occur when vesicles fuse with an invading apical membrane. Within the Caenorhabditis elegans excretory cell, which forms an intracellular tube, the exocyst vesicle-tethering complex is enriched at the lumenal membrane and is required for its outgrowth, suggesting that exocyst-targeted vesicles extend the lumen. Here, we identify a pathway that promotes intracellular tube extension by enriching the exocyst at the lumenal membrane. We show that PAR-6 and PKC-3/aPKC concentrate at the lumenal membrane and promote lumen extension. Using acute protein depletion, we find that PAR-6 is required for exocyst membrane recruitment, whereas PAR-3, which can recruit the exocyst in mammals, appears dispensable for exocyst localization and lumen extension. Finally, we show that CDC-42 and RhoGEF EXC-5/FGD regulate lumen extension by recruiting PAR-6 and PKC-3 to the lumenal membrane. Our findings reveal a pathway that connects CDC-42, PAR proteins, and the exocyst to extend intracellular tubes.

Highlights

Most organs contain tubes, which are used to transport gases and fluids from one site within the body to another
To determine if ZIF-1 expressed from the T28H11.8 promoter was sufficient to degrade ZF1-tagged proteins within the excretory cell, we introduced a high-copy array containing excretory cell cytoplasm (excP)::zif-1 into worms expressing a ZF1-tagged reporter protein, ZF1:: GFP::CDC-42
ZF1::GFP::CDC-42 was depleted below detectable levels within the excretory cell in larvae that inherited the excP::zif-1 transgenic array (Figure 1C), whereas expression of ZF1::GFP::CDC-42 persisted in other tissues

Summary

Introduction

Most organs contain tubes, which are used to transport gases and fluids from one site within the body to another. Born during the first half of embryogenesis, the H-shaped excretory cell contains four long canal arms that grow during larval stages to extend nearly the full length of the worm by the beginning of the L2 larval stage (Nelson et al, 1983; Sundaram and Buechner, 2016). An intracellular lumen initiates within the cell body and invades the length of each canal arm, functioning in osmoregulation (Buechner et al, 1999; Mancuso et al, 2012; Nelson and Riddle, 1984; Sundaram and Buechner, 2016). Vertebrate capillaries, as well as terminal and fusion cells of the Drosophila trachea and the Ciona notochord, are additional examples of cells containing intracellular tubes that are thought to form through an apical invasion mechanism (Denker et al, 2013; Gervais and Casanova, 2010; Herwig et al, 2011; Lenard et al, 2013)

Methods

Results

Conclusion